Inflatable cuffs have been proposed for applying occlusive pressure to a flow lumen of a patient's body, or for sealing between a medical instrument and a flow lumen of a patient's body. For example, an endotracheal tube may include an inflatable cuff that conforms to the contours of a patient's trachea when inserted into the trachea and inflated to seal a gap between the endotracheal tube and the trachea. Further, pressure indicators have been proposed for monitoring a fluid pressure within an inflatable cuff.
U.S. Pat. No. 4,727,887 (hereinafter “the '887 patent”) describes an artificial sphincter with an occlusion cuff for applying occlusive pressure to a flow lumen of a patient's body (e.g., a urethra). The '887 patent further proposes a combination hypodermic manometer including a piston assembly which is adapted for reciprocal movement through a fluid-filled sleeve. As the piston assembly of the '887 patent is moved through the sleeve, a bellows is compressed, thereby changing a height of fluid within a manometer fluidly coupled to the bellows. However, accuracy of the hypodermic manometer of the '887 patent may depend upon orientation of the manometer with respect to gravity, making it difficult to use with accuracy in practice. Moreover, a rupture or leak of the bellows poses the risk of mixing the manometer fluid with the fluid in contact with the occlusive cuff.
Pressure indicators including a bellows within a hollow housing made of a transparent material, such that an indicator mark on the bellows is visible through the housing, are known for use with pressure cuff devices. However, accuracy of such indicators may be sensitive to variations in the resilience of the bellows, which in turn is sensitive to variations in bellows geometric and material properties.
Accordingly, methods and apparatus are desired for indicating pressure in an inflatable cuff that are insensitive to geometric and material variations, and that are insensitive to the spatial orientation of the apparatus.